public class Example4_13 {
  public static void main (String args[]) {
    Circle1 circle = new Circle1();
    circle.setRadius(196.87);
    Tixing lader=new Tixing(3,21,9);
    Student zhang=new Student();
    System.out.println("zhang计算圆的面积:");
    double result = zhang.computerArea(circle);
    System.out.println(result);
    System.out.println("zhang计算梯形的面积：");
    result=zhang.computerArea(lader);
    System.out.println(result);
  }
}
